The present invention is directed to a hybrid dielectric material and a hybrid dielectric capacitor.
Capacitors are charge storage devices. They typically consist of two conducting electrodes and a layer of dielectric, insulating material located between the electrodes. When a battery or other voltage source is connected to a capacitor, polarization (charge separation) occurs in the dielectric layer, which develops a electric field across the capacitor, thereby storing a charge. When a charged capacitor is connected to a load device, discharge occurs.
The amount of charge that can be stored in a capacitor is determined by the following equation: C=k e0 A/d, where C=capacitance (in farads (F)), k=dielectric constant (the value of k depends on the dielectric property of the particular material that is used as the dielectric), e0=permittivity of vacuum, A=total area of the electrodes, and d=distance (or separation) between the two electrodes.
Capacitors are commonly used as local charge reservoirs for microprocessors. As the speed of microprocessors continues to increase, greater demands are placed on the power supply and voltage regulator to keep up with increasing transient current and voltage stability needs. If the current and voltage needs are not met, the microprocessor may exhibit reduced performance or may shut down. In order to solve this problem, and in order to meet the transient current and voltage stability demands, capacitors are placed close to the CPU, typically on the die package and on the motherboard. As high frequency computing operation demands more current, during the fast transient conditions, a charge stored in the capacitors is released to the CPU before the voltage regulator can respond.
One commonly used type of capacitor is a multi-layer ceramic capacitor (MLCC), which contains an inorganic ceramic such BaTiO3 as the dielectric material. A multi-layer ceramic capacitor has a high dielectric constant (up to 3000-4000) and can be prepared in a thin layer and a small form factor, which results in a significant performance enhancement. Today, multi-layer ceramic capacitors represent the largest sale among all capacitors. However, there are several disadvantages with multi-layer ceramic capacitors. The capacitance (dielectric constant) of BaTiO3-based dielectric material changes greatly with changes in temperature and voltage (it can vary as much as +/xe2x88x9250%). BaTiO3 is also a ferroelectric and piezoelectric material, which accounts for its relatively poor temperature and voltage performance. At high frequencies (above 1-10 GHz), BaTiO3 exhibits a significant capacitance roll-off. Moreover, manufacturing and processing costs for capacitors based on powdered ceramics such as BaTiO3 are high because high temperatures and laborious, time-consuming techniques such as tape casting and lamination are typically required.
Another commonly used type of capacitor is an organic polymer film capacitor, which uses an organic polymer as the dielectric material. Organic polymer film capacitors have advantages over multi-layer ceramic capacitors in that the organic polymer dielectric normally does not have ferroelectric nor piezoelectric properties, and therefore the dielectric constant has greater stability (better than 3-5%) under varying temperature, frequency and voltage conditions. In particular, organic polymer film capacitors are able to meet stringent capacitor tolerance conditions at high frequencies. Moreover, organic polymer film capacitors can be prepared at a lower temperature (less than 600-700xc2x0 C. vs greater than 1000xc2x0 C. for ceramic capacitors) using quicker and possibly less costly techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), spin-on/pyrolysis, spray/pyrolysis and the like. Much thinner layers can be prepared with polymer dielectric material than with ceramic material (0.1 xcexcm vs 1-2 xcexcm for ceramic dielectrics), which increases the capacitance density. However, organic polymer film capacitors have the disadvantage that the dielectric constant of the organic polymer dielectric is usually small (less than 20). The low dielectric constant limits the total capacitance that an organic polymer film capacitor can achieve. The reason why the capacitance of organic polymer film dielectric capacitors is low is that there are four different dielectric polarization mechanisms which contribute to overall polarizability of a material: (i) electronic (ii) ionic (3) di-polar and (4) space charge. BaTiO3-based dielectrics have all four mechanisms, and therefore, have a high dielectric constant. Organic polymer dielectrics, on the other hand, typically do not have di-polar polarization or ionic polarization, and therefore have a lower dielectric constant.